A network apparatus or the so-called embedded system (for example, a hub) is generally equipped with a cooling fan for quick dissipation of heat from its internal integrated circuit means. As illustrated in FIGS. 1 and 2, the cooling fan comprises a casing 90, and a fan blade assembly 91 pivotably mounted within the casing 90. The casing 90 has mounting holes at the corners thereof respectively and fixedly fastened to one upright side wall of the shell of the network apparatus 80 by screw bolts 71 and nuts 72. The upright side wall of the shell of the network apparatus 80 has air vents 81 corresponding to the fan blade assembly 91 in the casing 90 of the cooling fan. This cooling fan mounting arrangement has following drawbacks:
1. Because the fan casing 90 has a rectangular profile closely attached to the upright side wall of the shell of the network apparatus 80, the air vents 81 are made having a narrow, smoothly arched shape so as to prevent external object from being sucked into the inside of the fan casing 90. However, this design causes a high noise to be produced during the operation of the cooling fan. During the rotary motion of the fan blade assembly of the cooling fan, a part of outgoing currents of air or incoming currents of air is forced by the blocking area around the air vents 81 to flow back into the inside of the fan casing 90, thereby causing a negative pressure to be produced. Because of the presence of a negative pressure during the operation of the cooling fan, a turbulent flow of air is produced inside the fan casing 90, inducing a high noise.
2. Because the fan casing 90 is fastened to the upright side wall of the shell of the network apparatus 80 by screw bolts 71 and nuts 72, the screw bolts 71 receive much torsional force during the operation of the cooling fan, and the border area around each mounting hole at the fan casing 90 tends to be deformed.